Subbing composition for hydrophobic polymeric materials and subbed substrates



United States Patent 3,527,605 SUBBING COMPOSITION FOR HYDROPHOBIC POLYMERIC MATERIALS AND SUBBED SUBSTRATES Richard S. Fisch, St. Paul, and Albert W. Morgan, North St. Paul, Minn., assignors to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware No Drawing. Filed Jan. 17, 1966, Ser. No. 520,859 Int. Cl. G03c 1/78 US. CI. 96-87 12 Claims ABSTRACT OF THE DISCLOSURE A subbing composition capable of bonding a photosensitive silver halide gelatin emulsion to a hydrophobic film base which comprises from 20 to 80 weight percent of an epoxidized butadiene polymer having an epoxy equivalent from 80 to 200, from 20 to 80 weight percent of a normally solid, film forming polyester compatible therewith, and from 0.3 to 30 weight percent of an aldehyde-containing hardener for photographic emulsions, based on the weight of total solids. Also covers hydrophobic film base, including photographic films, containing such subbing compositions.

This invention relates to a novel subbing composition for hydrophobic polymeric materials, particularly polymeric materials suitable for use as photographic film base. In one aspect this invention relates to a single coat subbing system for oriented or unoriented polyester film. In another aspect this invention relates to a single coat subbing system for adhering a hydrophilic film forming material to a hydrophobic film, or conversely for adhering a hydrophobic film forming material to a hydrophilic film.

In the field of photography the conventional photographic film base materials are generally hydrophobic. In recent years cellulose acetate film base has been replaced to a considerable extent by polyester film, e.g. polyethylene terephthalate film. With the increasing use of new polymers in photographic substrates the problem of adhering hydrophilic photosensitive silver halide emulsions to the film base has become increasingly difiicult and complex. One approach to the solution of this problem has been to utilize a plurality of subbing or intermediate layers, the layer adjacent the hydrophobic film base being slightly more hydrophilic than the base material and the successive sub-bing layers being made increasingly more hydrophilic until the top surface of the subbing composite is sufficiently hydrophilic to accept the photosensitive emulsion. Although many attempts have been made to provide a subbing system having only a single layer or coating, innumerable problems have been encountered. When compatible materials, one of which provides good adhesion to a silver halide emulsion and the other of which has good adhesion to the film base, are blended to form a one-coat subbing layer, it is generally found that the normal adhesion of one material is aifected by the presence of the other. In addition, properties other than good dry adhesion are important in photographic constructions. Because of the various conditions encountered by photographic film during storage or development, the subbing construction must provide good adhesion between the photosensitive emulsion and the film base not only when dry but also when wet. It must maintain adhesion when exposed to processing solutions of high pH, as commonly encountered in photographic developers, and in processing solutions of low pH, as encountered in fixing or stopping baths. Moreover, the subbing construction should maintain the desired adhesion over extended periods of expo- "Ice sure to the various liquids employed in processing without significant alteration of the desired photographic characteristics of the photosensitive emulsion layer, which is normally quite sensitive to contamination.

It is an object of this invention to provide a subbing system requiring only a single coating.

A further object is to provide a process for subbing a hydrophobic film to provide a more hydrophilic surface thereon without the necessity for highly specialized or expensive processing techniques.

Still another object of this invention is to provide a photographic film having a single subbing layer between the photosensitive emulsion and the film base.

Yet another object of the invention is to bond a hydrophilic coating or layer to a hydrophobic film or substrate.

These and other objects are accomplished by this invention by the use of a homogeneous subbing composition comprising from 20 to weight percent of an epoxidized butadiene polymer having an epoxy equivalent from 80 to 200 (preferably from to from 20 to 80 weight percent of a normally solid, film forming polyester, preferably a polyester formed from a polybasic acid and a polyfunctional alcohol, having an adhesion to the hydrophobic substrate of at least 35 oz. per /2 inch (ASTM D-1000), preferably at least 45 oz. per /2 inch, the epoxidized butadiene and polyester being selected so as to be mutually compatible and transparent when in the form of a thin solid film, and an aldehyde-containing photographic hardener. The amount of hardener generally runs from 0.3 to 30 percent (preferably 3 to 5%) based on total solids Weight of the subbing composition, although the amount employed is not critical and can be varied over a wider range. For ease of coating such subbing compositions onto hydrophobic film, all of the major constituents of the subbing composition are preferably dissolved in a suitable inert organic solvent, preferably a solvent that does not significantly degrade or solubilize the hydrophobic substrate. When the polyesters are saturated (such as polyethylene terephthalate) chlorinated solvents, e.g. methylene chloride, may be usefully employed. When unsaturated polyesters, such as polyesters prepared from maleic acid are used as part of the subbing composition, a Wider variety of solvents can be employed, including methylene chloride and other chlorinated solvents, ketones (e.g. acetone), etc. The solids concentration of the various subbing constituents in the coating solution are selected to provide the desired viscosity and coating thickness and will to this extent be determined by the conditions selected for preparing the subbing layer and by the desired thickness of the subbing layer. Normally the solids concentration falls in the range of 2.5 to 15 weight percent.

Useful polyesters are characterized by their good adhesion to the hydrophobic film base and their compatibility with the epoxidized butadiene polymer. Of particular value are the relatively low molecular weight, normally solid, linear condensation polyesters prepared from saturated or unsaturated, aromatic or aliphatic dicarboxylic acids (or their halides) and a saturated or unsatu rated glycol (preferably a saturated glycol), including polyoxyalkylene glycols such as polyethylene glycol, which are preferably soluble in trichloroethylene to the extent of at least 0.5% by Weight at room temperature. If desired, the unsaturated polyesters may be cured in situ after the subbing film has been prepared by incorporating any of the well known peroxides, e.g. benzoyl peroxide, into the coating composition. Aldehyde-containing photographic hardeners for gelatin, such as mucochloric acid, formaldehyde, pyruvic aldehyde, heptaldehyde, crotonaldehyde, isobutyraldehyde, benzaldehyde, etc., are well known in the photographic literature and need not be discussed in greater detail. The epoxidized butadiene polymers preferably have a molecular weight between 5,000 and 500,000 and can be prepared by the well known reaction of a peroxy compound such as hydrogen peroxide or peracetic acid with an unsaturated butadiene or substituted butadiene homopolymer or copolymer, e.g. butadiene-styrene copolymers, *butadiene-acrylonitrile copolymers, etc.

The subbing composition of this invention may be used with a wide variety of hydrophobic film base materials, including cellulose ester film bases (e.g. cellulose acetate, cellulose triacetate, cellulose propionate, cellulose acetatepropionate, cellulose acetate butyrate, etc.), polypropylene, polyesters, and polyamides (e.g. as described in US. 2,071,250; 2,465,319 and 2,465,150) polyvinyl chloride, polystyrene, polyvinyl acetate, polycarbonate, vinyl chloride-vinyl acetate copolymers and others. Oriented polymers of ethylene glycol-terephthalic acid and/or isophthalic acid including those sold as Mylar, a trademark of El. du Pont de Nemours Co., are particularly preferred.

It should be appreciated that the subbing formulation may also contain minor amounts of materials useful in photographic film constructions and, in non-photographic applications where transparency is not a requirement, may contain various dyes, pigments, electrically conductive materials, fibers, etc. For photographic applications, the incorporation of materials which adversely affect the photosensitive properties of the silver halide gelatin emulsion and which tend to migrate into the adjacent emulsion layer should be avoided.

In the following illustrative examples all parts are by weight unless otherwise noted.

EXAMPLE 1 10 grams of unsaturated polyester (50% phthalic acid, 25% adipic acid, 25% maleic acid and ethylene glycol; polymerized in methyl methacrylate and containing 25% methyl methacrylate in the polymer), 10 grams of epoxidized polybutadiene (epoxy equivalent of 122), 0.03 gram of benzoyl peroxide, and 2 grams of mucochloric acid were mixed as a 10% solution in methyl ethyl ketone. The solution was coated (0.05 mil wet coating thickness) onto a mil polyethylene terephthalate film and allowed to dry. A silver halide emulsion overcoating was then applied and allowed to dry. The construction had very excellent dry adhesion (over 45 oz. per /2 inch as measured by ASTM test D-1000), was unaffected by water immersion for over 3 days and resisted photographic processing. The emulsion coating had good scratch resistancel A similar construction, omitting the mucochloric acid, had decidedly inferior resistance to water immersion.

EXAMPLE 2 grams of the unsaturated polyester of Example, 1, 10 grames of epoxidized polybutadiene (epoxy equivalent of 122), 0.03 gram benzoyl peroxide, 3.2 grams mucochloric acid and 1.6 grams resorcinol were mixed as a 10% solution in methyl ethyl ketone, and the resulting solution was coated (0.5 mil wet coating thickness) onto 5 mil polyethylene terephthalate photographic film base. After the coating was dry a silver halide emulsion was overcoated and dried. Both dry adhesion and wet adhesion were excellent. The construction resisted water immersion for up to 8 days, hydroquinone-paraformaldehyde developer for up to 8 days, and sodium thiosulfate fixer for up to 8 days.

EXAMPLE 3 Example 2 was repeated with the addition of 0.015 gram dimethylaniline. Excellent results were obtained in all adhesion tests.

EXAMPLE 4 Example 2 was repeated with the reduction of the mucochloric acid content to 1.6 grams and the resorcinol 4 content to 0.8 gram. Results in all adhesion testing were excellent.

EXAMPLE 5 Example 4 was repeated without resorcinol. Results in adhesion testing were good with only slightly less wet adhesion than Example 4.

EXAMPLE 6 10 grams of a saturated polyester of ethylene glycol and terephthalic/isophthalic acid (/45 weight ratio) having 8500 p.s.i. tensile strength, 4% elongation, 71 C. softening point, and 1.7 refractive index; 10 grams of epoxidized polybutadiene (epoxy equivalent of 126) and 1.6 grams of mucochloric acid were mixed as a 10% solution in methylene chloride. This solution was coated (0.5 mil wet coating thickness) onto 5 mil polyethylene terephthalate photographic film base. After the coating was dry, silver halide gelatin emulsion was overcoated and dried. Dry and wet adhesion were excellent. Resistance to hydroquinone-paraformaldehyde developers and fixer as well as to water was outstanding.

EXAMPLE 7 Example 6 was repeated with the addition of 0.8 gram resorcinol. Very good adhesion, both wet and dry, was obtained.

EXAMPLE 8 Repeating Example 6 with 20 grams of the epoxidized polybutadiene, excellent ;wet and dry adhesion was obtained.

EXAMPLE 9 Example 8 was repeated with the addition of 0.8 gram resorcinol. Excellent wet and dry adhesion was obtained.

EXAMPLE 10 Repeating Example 9 with various aldhehydes substituted for mucochloric acid, outstanding wet and dry adhesin was obtained with pyruvic aldehyde, heptalde'hyde, croton aldehyde, isobutyl aldehyde, benzaldehyde and glyoxal.

EXAMPLE 11 The following subbing compositions were coated (0.5 mil wet thickness) onto polyester photographic film base stock:

10 grams unsaturated polyester of Example 1 10 grams epoxidized polybutadiene (epoxy equivalent of 0.03 gram benzoyl peroxide 0.015 gram dimethylaniline 1.6 grams mucochloric acid 0.08 gram resorcinol methyl ethyl ketone to make 10% solids 10 grams saturated polyester of Example 6 15 grams epoxidized polybutadiene (epoxy equivalent 1.6 grams mucochloric acid 0.08 gram resorcinol trichloroethylene to make 10% solids 20 grams saturated polyester of Example 6 10 grams epoxidized polybutadine (epoxy equivalent of 3 grams mucochloric acid 1.5 grams resorcinol trichloroethylene to make 10% solids Samples coated with Composition A, B, and C and a sample of commercially subbed polyester photographic film base were coated with a silver halide-gelatin emulsion.

Speed (relative log Sample Fog (density) exposure units) Commercial controL- 0. 12 9.

A 0. 12 9. 4 B 0. 18 9. 8 C 0. l8 9. 4

Wet adhesion of the commercial control was 75 to 93%. Sample A had a wet adhesion from 52 to 87%, and samples B and C had from 95 to 99% wet adhesion. Samples A-C were comparable or superior to the commercial control in color, dry haze, wet haze and ability to withstand developer, fixer and water immersion tests. None of the samples had a brittleness problem.

EXAMPLE 12 EXAMPLE 13 Excellent adhesion was obtained when the subbing composition of Example 11A was coated onto polypropylene film base and a silver halide gelatin emulsion was coated thereon. The construction was unaffected by water immersion for 8 days.

As used herein, wet adhesion is determined by the procedures set forth in ASTM Bulletin (February 1959), pages 4854. Speed measurements were made in accordance with procedures presented in the 1956 Bulletin of the Technical Association of the Graphic Arts, pages 167- 182.

Various other embodiments of the present invention will be apparent to those skilled in the art without departing from the spirit or scope thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A transparent subbing composition capable of bonding a photosensitive silver halide gelatin emulsion to a hydrophobic film base which consists essentially of from 20 to 80 weight percent of an epoxidized butadiene polymer having an epoxy equivalent from 80 to 200, from 20 to 80 weight percent of a normally solid, film forming, condensation polyester compatible therewith, said polyester having an adhesion to said film base of at least 35 oz. per /2 inch, and from 0.3 to 30 weight percent of an aldehyde-containing hardener for photographic emulsions, based on the weight of total solids.

2. The subbing composition of claim 1 in which said composition contains up to about 15 Weight percent of said constituents dissolved in an inert organic solvent.

3. The subbing composition of claim 1 in which said polyester is a condensation product of a polycarboxylic acid and a polyfunctional alcohol.

4. The subbing composition of claim 1 in Which said polyester is saturated.

5. The subbing composition of claim 1 in which said polyester is unsaturated.

6. The subbing composition of claim 5 in which is incorporated a peroxide curing agent for said unsaturated polyester. I

7. A hydrophobic film base on which is superimposed a transparent subbing coating consisting essentially of from 20 to weight percent of an epoxidized butadiene polymer having an epoxy equivalent from 80 to 200, from 20 to 80 weight percent of a normally solid, film forming, condensation polyester compatible therewith, said poiyester having an adhesion to said film base of at least 35 oz. per /2 inch, and from 0.3 to 30 weight percent of an aldehyde-containing hardener for photographic emulsions.

8. The subbed hydrophobic film base of claim 7 in which said film base is polyethylene terephthalate.

9. A photographic film construction having a hydrophobic film base, and a photosensitive silver halide gelatin layer directly bonded to said hydrophobic film base with a light transparent subbing composition consisting essentially of from 20 to 80 weight percent of an epoxi dized butadiene polymer having an epoxy equivalent from 80 to 200, from 20 to 80 weight percent of a normally solid, film forming, condensation polyester compatible therewith, said polyester having an adhesion to said film base of at least 35 oz. per /2 inch, and from 0.3 to 30 Weight percent of an aldehyde-containing hardener for photographic emulsions.

10. The photographic film construction of claim 9 in which said polyester per se has an adhesion of at least 35 oz. per /2 inch to the said hydrophobic film base material.

11. The photographic film construction of claim 9 in which said hydrophobic film base is a polyester of the polyethylene terephthalate type.

12. The photographic film construction of claim 9 in which said hydrophobic film base is oriented Mylar.

References Cited UNITED STATES PATENTS 3,397,988 8/1968 Paesschen et a1 96-114 3,084,137 4/1963 NOWlin et a] 260-40 3,212,897 10/1965 Secrist 96-87 3,216,825 11/1965 Caldwell 96-87 NORMAN G. TORCHIN, Primary Examiner I. R. HIGHTOWER, Assistant Examiner US. Cl. X.R. 260-348 

